Computer Systems and Networks

The internet is a network of networks. Devices communicate because they follow protocols: agreed rules for formatting, addressing, transmitting, routing, and interpreting messages.

Large messages are divided into packets. Packets may travel different routes and be reassembled by the destination system.

IP addresses help route packets to a destination. Domain names are human-friendly names that must be translated to IP addresses through DNS.

Fault tolerance means a system can continue functioning when part of it fails. Redundant paths, replicated services, backups, and distributed design can improve availability.

The internet was designed so packets can route around many failures, but that does not mean every service is always reachable or every packet is guaranteed to arrive instantly.

Scalability asks whether a system can keep working as the number of users, devices, or messages grows.

Parallel computing uses multiple processors or cores at the same time. Distributed computing uses multiple networked computers working together.

Dividing a task can reduce time when subtasks can happen independently, but coordination, communication, and combining results add overhead.

Some tasks cannot be sped up much because parts must happen in sequence. The best answer depends on the task structure.

AP CSP cybersecurity focuses on practical protection: authentication, authorization, encryption, safe communication, malware awareness, phishing, certificates, and secure behavior.

Encryption protects confidentiality by making data unreadable without a key. HTTPS uses encryption to protect web traffic in transit and helps users confirm they are communicating with the intended site.

Good security is layered. Strong passwords, MFA, updates, backups, cautious clicking, and least privilege reduce different parts of risk.